Method and system for determining air turbulence using bi-static measurements

ABSTRACT

A method and system for determining atmospheric disturbances or turbulence is disclosed. The system includes a plurality of sensor arrays, including at least one sensor element, distributed in a predetermined manner. Each of the sensor elements is in communication with a corresponding receiving system that is operable to receive and process energy received from the aircraft. A determination is then made regarding air turbulence by determining a rate of change of signal phase among selected sets of signals received at the receiving systems. A turbulence map is then determined from the determined rate of change of the phase and the angle of the received signal. When the rate of phase change exceeds known levels an indication of turbulence is made.

CLAIM FOR PRIORITY

[0001] This application is a continuation-in-part of co-pending patentapplication Ser. No. 10,067,154 entitled METHOD AND SYSTEM FORDETERMINING AIR TURBULENCE USING BI-STATIC MEASUREMENTS.

FIELD OF THE INVENTION

[0002] This invention is related to the detection of air turbulence andmore specifically, to a method and system for determining air turbulenceusing bi-static measurements.

BACKGROUND OF THE INVENTION

[0003] In air travel, the most hazardous phase that an aircraftexperiences is the landing or takeoff. In these phases, an aircraft isvulnerable to unexpected changes in the surrounding environment. Forexample, wind shears or other sudden or violent changes in the directionof the wind can cause a misalignment of the aircraft with respect to therunway. Furthermore, sudden drops in air pressure can cause the aircraftto suddenly lose altitude at a time when excess altitude is notavailable.

[0004] In addition to natural changes in the surrounding environment,aircraft landings and takeoffs also create vortexes or wake disturbancesin the environment behind the aircraft that may affect the operation ofa next and subsequent aircraft. Minimum required distances betweenaircraft have been established in order to reduce the effects of thevortex on the next or subsequent aircraft, hence, improving their safetyHowever, such required minimum distances are set to accommodateworst-case conditions and are longer than necessary.

[0005] Knowledge of the disturbances or turbulence in the aircraft'ssurrounding environment can be used to improve aircraft safety and canalso be used to reduce the minimum distance needed between aircraft,thus, increasing airport efficiency.

[0006] Hence, there is a need for determining disturbances or turbulencein the atmosphere surrounding an aircraft. In one aspect, knowledge ofwake disturbances in the area around the ends of aircraft runways isimportant. In another aspect, knowledge of wake disturbance immediatelyahead of an aircraft is similarly important.

SUMMARY OF THE INVENTION

[0007] A method for determining atmospheric disturbances or turbulencepreceding an aircraft or induced by an aircraft is disclosed. The methodincludes receiving a signal from a plurality of sensor arrays, eachincluding at least one sensor element, distributed in a predeterminedmanner. Each of the sensor elements is in communication with acorresponding receiving system that is operable to receive and processelectromagnetic energy that is emanating from an approaching ordeparting aircraft. A determination is then made regarding air or waketurbulence by determining a rate of change of signal phase amongselected sets of signals received at the receiving systems. A turbulencemap is then determined from the determined rate of change of the phaseand the angle of the received signal. When the rate of phase changeexceeds known levels an indication of turbulence is made. In anotheraspect of the invention, each of the sensor arrays can include aplurality of sensor elements, which may be used to determine a preciseangle of arrival of the received signal. In still another aspect of theinvention, sensor arrays may be located on-board an aircraft to monitorturbulence immediately before it.

BRIEF DESCRIPTION OF THE FIGURES

[0008]FIG. 1 illustrates a perspective view of aircraft approaching arunway further illustrating an exemplary distribution of sensor arraysin accordance with the principles of the invention;

[0009]FIGS. 2a-2 b illustrate phase changes in non-turbulent andturbulent conditions, respectively;

[0010]FIG. 3 illustrates an exemplary process flow for determiningturbulence in accordance with the principles of the present invention;

[0011]FIG. 4a illustrates a block diagram of an exemplary systemconfiguration in accordance with the principles of the presentinvention;

[0012]FIG. 4b illustrates a block diagram of a second exemplary systemconfiguration in accordance with the principles of the presentinvention;

[0013]FIG. 5 illustrates a block diagram of an exemplary signalprocessing system in accordance with the principles of the presentinvention;

[0014]FIG. 6 illustrates a block diagram of an exemplary receiver/signalestimator as used in the present invention;

[0015]FIG. 7 illustrates a block diagram of an exemplary differentialsignal phase and phase rate estimator in accordance with the principlesof the present invention;

[0016]FIG. 8 illustrates a block diagram of an exemplary Wake spectralanalyzer in accordance with the principles of the present invention;

[0017]FIGS. 9a-9 d illustrate exemplary placements of sensor elements inaccordance with the principles of the present invention;

[0018]FIG. 10 illustrates a flow chart of an exemplary process fordetermining phase difference;

[0019]FIG. 11 illustrates a flow chart of an exemplary process fordetermining phase rate of change;.

[0020]FIG. 12 illustrates a second embodiment of an exemplary airturbulence system in accordance with the principles of the invention;and.

[0021]FIG. 13 illustrates a prospective view of a system using aspatially-notched antenna pattern in accordance with the principles ofthe invention.

[0022] It is to be understood that these drawings are solely forpurposes of illustrating the concepts of the invention and are notintended as a level of the limits of the invention. It will beappreciated that the same reference numerals, possibly supplemented withreference characters where appropriate, have been used throughout toidentify corresponding parts.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0023]FIG. 1 illustrates a perspective view 100 of an exemplary airturbulence, or vortex column 105 immediately forward of an aircraft 110approaching runway 115. FIG. 1 may similarly illustrate a perspectiveview of an air turbulence or vortex column induced by a departingaircraft. In either aspect of the invention, the illustrated groundbased sensor arrays and corresponding receiving systems 120, 121, 122,124, and 125 are positioned in locations at an end of runway 115 todetect and determine air turbulence in the vicinity of the runway end.While only five sensor arrays/receiving systems 120-125 are shown in theillustrated example, it will be appreciated that the system disclosedmay be easily expanded to include any number of receiving systems.Furthermore, while the sensor arrays/receiving systems 120-125 are shownin the example co-located in the vicinity of the runway, it will beappreciated that the sensor arrays and corresponding receiving systemsmay be remotely located. In this case, corresponding receiving systemsmay be located at one or more central locations and connected to acorresponding sensor array through a wired or wireless network. Theallowable distance between sensor array and corresponding receivingsystems as would be known depends upon factors such as antenna gain,signal strength, receiver sensitivity, signal amplification, etc.

[0024] Returning now to FIG. 1, the illustrated sensor arrays/receivingsystems 120-125 detect electromagnetic energy that originates oremanates from approaching or departing aircraft 110 and provides thereceived signal energy to a corresponding receiving system for isolationof a desired signal. A received signal path length, illustrated as130-135, between aircraft and sensor array/receiving systems depends onthe position of aircraft 110, the locations of sensor array/receivingsystems, 120-125, and the spatial angle between aircraft 110 and thesensor array.

[0025]FIG. 2a illustrates the constant phase of the signals received atarray plane 140 containing array sensors/receiving systems 120-125 whenno turbulence exists in the signal path between the aircraft and arraysensors/receiving systems 120-125. The signal received at any of thereceiving systems may be represented as:

S _(r) =K sin(ωt+φ)  [1]

[0026] wherein

[0027] S_(r) is the received signal;

[0028] K is a constant;

[0029] ωt is representative of the transmitting frequency; and

[0030] φ is representative of the phase angle induced by the path length

[0031] between the aircraft and sensor array.

[0032] In the determination of the instantaneous received frequency of adynamically moving target, the received signal frequency is furtherinfluenced by the well known principle of Doppler shift and isdetermined as

S _(r)(t)=K sin(ωt+φ(t))  [2]

[0033] where

[0034] S_(r)(t) is the received signal as a function of time; and

[0035] φ(t) is representative of the time variant phase angle induced bythe changing path length.

[0036]FIG. 2b illustrates the non-uniform phase of signals traversingair turbulence existing between the aircraft 110 and plane 140containing array sensors/receiving systems 120-125. Turbulence oratmospheric index of refraction variations are influenced by knownchanges in air pressure, temperature, and moisture. Aircraft vortices,in particular, produce changes in all three parameters. Changes inatmospheric refractive index in turn produce changes in propagationdelay and direction that manifest themselves in terms of distortions inthe received signal wavefront and phase. The received frequency isfurther influenced by the changing atmospheric conditions and may bedetermined as:

S _(r)(t)=K sin(ωt+φ(t)+τ(t))  [3]

[0037] where

[0038] τ(t) is representative of the time variant change in phase causedby changing atmospheric conditions.

[0039]FIG. 3 illustrates an exemplary process flow 200 wherein each of aplurality of differential path determinations, determined by illustratedprocessors 210, 220, 230 are provided to processor 240. Differentialpath processor 210, for example, determines an estimation of a signalphase at each of a plurality of sensor arrays. In this illustrativeexample, differential phase estimates are obtained using two sensorarrays. The phase estimates are then applied at processing module 216 toblock 216 to resolve signal differences and determine phase estimatesalong differential signal paths to each sensor array. At processingblock 217, an angle of arrival may be determined to define a signalpath. The accuracy and precision of the determined angle of arrivaldepends on the number and position of sensor elements within each sensorarray. At processing block 218, a level of turbulence is determinedbased on a spectral estimation of the rate of phase change along adefined signal path. At processing block 240 an image of turbulence inthe region along the defined signal path is prepared from each of thedetermined differential path turbulence estimates. At processing block250, an image of the turbulence estimates may be displayed to a groundand/or air based operator.

[0040]FIG. 4a illustrates a block diagram of an exemplary air turbulencemonitoring system 300 for detecting and determining air turbulence inaccordance with the principles of the invention. In this exemplarysystem, a single sensor element 305 is shown contained within sensorarray 330. Sensor elements are positioned to provide a determination ofthe phase of the received signal using known methods. In a preferredembodiment, the phase of the received signal is resolved unambiguously.Each of the plurality of sensor arrays 330 are further in communicationwith a corresponding receiving and signal vector estimator system 340,which provides a corresponding detected and estimated signal toprocessor 345. Processor 345 is operable to process the received signalsand determine a differential phase, an estimate of phase rate, andpotential turbulence and wake.

[0041] Receiving subsystems that receive and process electromagneticsignals originating or emanating from, in this case, a same source arewell known in the art and need not be discussed in detail herein. Thedetected electromagnetic signals may be selected from an on-boardsignal, such as IFF, altitude transponder, navigation transponder, VHFradio, UHF radio, FLIR, weather RADAR, or a ground based signal, such asground based RADAR, e.g., Air Traffic Control Radar Beacon System(ATCRBS). Furthermore, ultraviolet, visible, or infrared light sources,such as landing lights, reflected or sourced light are representative ofelectromagnetic energy that may also be used when received by sensorelements 305 and receiving systems operable to process suchelectromagnetic radiation.

[0042]FIG. 4b illustrates a block diagram of a second and preferredaspect of the present invention. In this example, each of the sensorarrays 330 contains a plurality of sensing elements 305. In this casethe plurality of sensing elements may be predeterminedly positioned todetermine an angle of arrival of the received signal and a compositephase value for the signal received among the sensor elements. In apreferred embodiment of the invention, sensor elements 305 arepositioned within each sensor array 330 using well-known interferometricmethodology for determining unambiguous signal angle of arrival.

[0043]FIG. 5 illustrates a block diagram 320 of processor 345. In thisillustrated block diagram received signals from each sensor element 305within each sensor array 330 are provided to a correspondingreceiver/signal estimator 340. Selected signals from receiver/signalestimator 340 are then provided to differential phase and phase rateestimator 350. The output of phase rate estimator 350 is then providedto spectral analyzer 365. The output of spectral analyzer 365 is thenprovided to processor 370. Processor 370 then determines turbulence andwakes based on the rate of change of the measured phase of the receivedsignals. As will be appreciated the number of sensor arrays 330 andreceiving systems 340 may be easily increased to any number ofsubsystems by incorporating additional subsystems in parallel withoutchanging the scope of the invention.

[0044] As is further illustrated, a signal 325 is selected from at leastone selected receiving system and is provided to each of thereceiving/signal estimators 350. Signal 325 is then used as a referencesignal to determine a phase measurement for each of the receivedsignals. In a second aspect of the invention, a signal 325 from eachreceiving system may be provided to every other receiving system todetermine phase measures with regard to different reference signals.

[0045]FIG. 6 illustrates a block diagram of an exemplary receiver/signalestimator 340. In this case, a plurality of sensor elements 330 a, 330b, 330 c, through 330 n are contained within sensor array 330. Sensorelements 330 a-330 n preferably are distributed at locations withrespect to one another to determine an unambiguous angle of arrival.Determination of unambiguous angle of arrival of a received signal maybe determined using known methods, e.g., interferometric methods.

[0046] As illustrated, each sensor element 330 a-330 n provides adetected signal to a corresponding receiving system 342 a-342 n.Further, in the illustrated case, first receiving system 342 a isselected as a reference signal source from which all other signalsdetected at sensor elements 342 b-342 n are processed. The processedsignal of the selected reference receiver 342 a and the signals detectedby each of the remaining receiving systems 342 b-342 n are pair-wiseapplied to corresponding coherent signal product generators 344 b-344 n.For example, the output of receiving system 342 b and reference signal325 are applied to signal product generator 344 b. Although the outputsof the receiving systems 342 b-342 n are depicted as being pair-wiseapplied to corresponding coherent signal product signal generators 344b-344 n, it would be appreciated that any number of signals may beapplied to a corresponding coherent signal product generator.

[0047] The output of each coherent signal product generator 344 b-344 nis then applied to a signal vector estimator processor 346. Signalestimator processor 346 determines refined signal vector valuesrepresentative of the signals received by sensor elements in array 330.Further, each of the signals 348 b-348 n is represented as having anin-phase, “I” and quadraphase “Q” component. Signals 348 b-348 n mayalso be represented as in a matrix form having a determined amplitudeand phase value.

[0048]FIG. 7 illustrates a block diagram of an exemplary differentialphase and phase rate estimator 350. In this exemplary block diagram,each of the signal vectors 348 b-348 n of at least two signal estimators340 are provided to differential path phase difference processor 352 todetermine a differential path phase difference between the providedsignal vectors. In a preferred embodiment, the resultant differencesignal vectors are decomposed into their complex in-phase andquadrature-phase signal components, represented as I and Q respectively.The in-phase components of the provided signal vectors are providedconcurrently to both inputs of multiplier 353, to differentiator 355 andto multiplier 354. The output of multiplier 353 is thus representativeof the square of the I component. The output of differentiator 355 isthus representative of the derivative of the I component, represented as

. Similarly, the quadrature components of the provided signal vectorsare provided to both inputs of multiplier 357, to differentiator 356,and to multiplier 358. The output of multiplier 357 is representative ofthe square of the quadrature component and the output of differentiator356 is representative of the derivative of the quadrature component,represented as

. The I and Q which are provided to multipliers 354 and 358,respectively, are then multiplied by corresponding differentiated Q andI signals, i.e.,

and

, respectively. The difference of the outputs of multiplier 354 and 358is then determined by subtractor 360. The square of the I and Qcomponents are then provided to adder 359 to produce a signalrepresentative of the sum of the square of the I and Q components, i.e.,I²+Q². The output of subtractor 360 and the square of the I and Qcomponents is then provided to divider 361. A differential path phaserate signal may then be determined as:$\frac{{Q\quad \overset{o}{I}} - {I\quad \overset{o}{Q}}}{I^{2} + Q^{2}}\quad {where}\quad \overset{o}{I}\quad {and}\quad \overset{o}{Q}$

[0049] are first derivatives of in-phase and quadrature phase componentsof the provided signal vectors.

[0050] Differential phase, interferometer-receiving systems arepreferably used for detecting phase rate changes. By computing thedifferential rate of phase change from at least two slightly differingpaths between a common source and each of two interferometer receivingelements, the phase effects that are common to both paths are cancelledand, hence, the differences between paths is accentuated. The ability tomeasure the degree of differential phase fluctuations between at leastpairs of signal paths and recorded histories of these fluctuationsrelated to respective path geometries allows regions of fluctuations tobe determined, tracked and mapped.

[0051]FIG. 8 illustrates a block diagram of an exemplary wake spectralanalyzer 365. In this example, a differential signal is applied tospectral filter 366. Spectral filter 366 separates the phase ratespectrum of a wake-induced phase values from the principally staticnon-wake phase values. In one aspect, a Fourier Transform or FastFourier Transform (FFT) may be implemented in the processing of spectralfilter 366. The output of spectral filter 366 is applied to spectralcell normalizer 367, referred to as spectral cell normalization, whichnormalizes the determined differential signal across time and frequency.The output of normalizer 367 is then applied to turbulence thresholddetector 368. The output of turbulence detector 368 is then applied toprocessor 370.

[0052]FIGS. 9a-9 d illustrate exemplary sensor array configurations.FIGS. 9a-9 c illustrate exemplary configurations wherein sensor elementsare linearly positioned. FIG. 9d illustrates an array configurationwherein the sensor elements are positioned along two axii. Morespecifically, FIG. 9a illustrates a plurality of sensor arrays 900containing two sensor elements 305 linearly aligned in each array. FIG.9b illustrates a plurality of sensor arrays 920 wherein three sensorelements 305 are linearly aligned. In a preferred aspect, thepositioning of sensor elements 305 is determined in accordance with wellknown interferometric methods. FIG. 9c illustrates a plurality of sensorarrays 940 having four sensor elements 305. As would be understood, asthe number of sensor elements or the spacing between sensor elementsincreases, the ability to unambiguously determine angle of arrival andsignal phase increases. FIG. 9d illustrates a plurality oftwo-dimensional sensor arrays 960 containing sensor elements 305positioned in two dimensions. This position allows for an improveddetermination of the angle of arrival of the received signal. Althoughnot shown, it would be understood that sensor elements may further beoriented or positioned in three dimensions to further improve thedetermination of received signal angle of arrival. While FIGS. 9a-9 dillustrate exemplary positions of sensor elements, it is not intendedthat only those sensor element orientations shown are within the scopeof the invention. Rather, any number of sensor elements or sensorelement positions may be used without altering the scope of theinvention.

[0053]FIG. 10 illustrates a flow chart 1000 of an exemplary processingto determine air turbulence in accordance with the principles of thepresent invention. In this case, the phase of the signal received at anI-th receiving system is established as a reference phase signal, atblock 1010. The phase of the signal received at a next or subsequent(j-th) receiving system is then obtained, at block 1020. The differencebetween the signal phases received at the selected i-th and j-threceiving system is then determined, at block 1030. A determination ofthe rate of change of the signal phase difference is then determinedbetween the difference in phases at two known times or time periods atthe I-th and j-th systems is made and stored at block 1040.

[0054] A next/subsequent receiving system is then selected, at block1050. A determination is then made at block 1060 whether all j-threceiving systems have been selected. If the answer is in the negativethen the phase of the next/subsequent receiving system is obtained atblock 1020. Accordingly, the phase of the signal received at eachnext/subsequent receiving system is evaluated with regard to a selectedreference signal phase from an I-th receiving system. In one aspect ofthe invention, if the answer at block 1060 is affirmative, then a map ofturbulence over the I-th/j-th receiver system combinations may bedetermined at block 1090. As an example, in this aspect of theinvention, a turbulence map may be determined based on phase measurementdeterminations using receiving systems combinations 1^(st)/2^(nd),1^(st)/3^(rd), 1^(st)/4^(th), through 1^(st)/n^(th) receiving systems.

[0055] In a second aspect of the invention, and one that is illustratedin FIG. 10, if a the answer at block 1060 is in the negative, then anext I-th receiving system may be selected at block 1070. Adetermination is then made at block 1080 whether all the I-th receivingsystems have been selected. If the answer is in the negative then thephase of the I-th receiving system is established as a reference atblock 1010. The process of determining rate of phase change between thereference phase value at the selected I-th receiving system and thesignals received at the j-th receiving system is repeated for selectedI-th and j-th receiving systems.

[0056] If, however, the answer at block 1080 is affirmative, then a mapof turbulence over the I-th/j-th receiver system combinations may bedetermined at block 1090. As an example, in this aspect of theinvention, a turbulence map may be determined based on phase measurementdeterminations using receiving system combinations 1^(st)/2^(nd),1^(st)/3^(rd), 1^(st)/4^(th), . . . , 1^(st)/n^(th), 2^(nd)/3^(rd),2^(nd)/4^(th), . . . ,2^(nd)/n^(th), 3^(rd)/4^(th), . . .,3^(rd)/n^(th), etc. As would be appreciated, a determination of an airturbulence mapping may also be obtained from the phase difference ofselected receiving systems.

[0057] Although the exemplary processing illustrated depicts determiningrate of phase change between two same received signals, it would beappreciated that rate of phase change among three or more same receivedsignals can also be determined and used in mapping the determinedturbulence.

[0058]FIG. 11 illustrates a flow chart of an exemplary processing 1040for determining rate of phase change between a signal received at anI-th receiving system and the signal received at a j-th receivingsystem. In one aspect of the invention, the instantaneous phase of thesignal received at the I-th receiving system is determined at a firsttime, at block 1042 and the instantaneous phase of the signal receivedat the j-th receiving system is determined at a concurrent time, atblock 1043. The difference between the two instantaneous phases at thefirst time is then determined at block 1044. The determined difference,at the first time, is then compared to an instantaneous phase differenceobtained for the same received signal at a previous time at block 1045.When the difference in the instantaneous phase from a first time to aprevious time exceeds a known limit, then an indication of turbulencemay be recorded at block 1046. As would be appreciated, a known limitvalue may be independently associated with each receiving systemcombination. In another aspect of the invention, the rate of phasechange over a known time period may be used to determine a measure ofair turbulence. In this aspect of the invention, a measure of the phasechange over a known time period is determined for the signal received atthe i-th receiving system. For example, a measure of the signal phasechange may be an average, a weighed average, a mean, a median, etc., ofphase change over a selected time period. As would be understood, thedetermination of an average and weighted average, etc., must considerthe 360/0 degree crossover of phase measurements. In still anotheraspect of the invention, a measure of phase change may be determined asa polynomial relation that provides a minimum mean square error of thesignal phase data collected during the selected time period. A similarmeasure of phase change is determined over the selected time period forthe signal received at the j-th receiving system. The rate of phasechange may then be determined as the difference between the differencebetween the two polynomial relations at the two receiving systems overthe first time period and the difference in the two polynomial relationsrepresentative of the two signal phases at the same receiving systemsover a previous known period. When the rate of phase change from onetime period to a previous time period exceeds a known limit, then anindication of turbulence is recorded. Methods of determining leastsquare fit polynomials and operations on polynomial are well known inthe art and need not be disclosed herein. As would be appreciated,selected time periods may be disjointed, wherein the phase data of onetime period is independent of an adjacent period. Or the selected periodmay be a sliding period wherein current phase data replaces phase olderdata in a first in/first out mode.

[0059]FIG. 12 illustrates a second embodiment of the present invention,wherein sensor arrays are distributed in predeterminedly locatedpositions to detect and process electromagnetic signal energyimmediately before aircraft 110. In this illustrative example, sensorarrays 350 are positioned in the aircraft nose and along the forwardedge of each wing 1200, 1210. In still another aspect of the invention,a sensor array 350 may be mounted vertically, e.g., on the verticalstabilizer 1220, to provide a two-dimensional measure of turbulenceimmediately ahead of aircraft 110.

[0060] In one aspect of the invention, as shown in FIG. 1, each of thereceiving systems includes an antenna that is positioned or directed insubstantially a co-linear fashion with a direct signal path of a desiredsignal transmitted or reflected from the target aircraft. In thisaspect, the main beam of the antenna pattern is directed or positionedin space to receive a substantially maximum level of energy from thedesired signal. As would be appreciated, the receiving system antennamay also be movable to enable the receiving system to continuouslyreceive a substantially maximum signal energy as the target aircraftcontinues along its flight path.

[0061] In another aspect of the invention, the antenna pattern of areceiving system may be mechanically positioned or electronicallyaltered such that a spatial null is created around the direct signalpath of the desired signal transmitted or reflected from the targetaircraft. FIG. 13 illustrates a spatial antenna pattern 1310electronically altered to create a central spatial null 1315 to avoidreception of a direct beam of a desired signal transmitted or reflectedfrom the target aircraft. In this illustrated aspect of the inventionantenna pattern 1310 is electronically altered using known phaseaddition and difference circuits to fabricate antenna pattern 1310 toexhibit an annulus of sensitivity 1320 about spatial null or receptionhole 1315. More specifically, an annulus of sensitivity describes aregion of interest that includes possible (weak) signal paths fromatmospheric refractions of interest but excluding the direct, intensepath from the source (still used as a source for our “reference”signal).

[0062] The creation of spatial null 1315 around the direct path of thedesired signal is analogous to viewing the sun's cornea in that a disk,appropriately sized and placed in the direct path of the sunlight,blocks the extremely bright, directly viewable sunlight and enablesviewing of lower-powered surrounding cornea. This method of viewing thecornea is necessary due to the exceedingly large optical dynamic rangepresented to the viewer with the much higher power of the directlyviewed sunlight washing-out and/or obscuring the lower power view of thecornea. Similarly, formation of null 1315 and annulus 1320 of pattern1310 in accordance with an aspect of the present invention permits lowerpower refracted signals 1325 to be detected and processed by thecorresponding receiving system.

[0063] In a preferred embodiment, the antenna off-axis position orphase-altered pattern fabricates a spatial-nullity 1315 sized tosubstantially eliminate, prevent, or preclude reception of signal energyfrom the direct path. Hence, rather than processing a direct pathsignal, lower power refracted signals 1325 are capable of being detectedand processed by the corresponding receiving system.

[0064]FIG. 13 further illustrates an exemplary system operation of asystem using spatial-nulling antennas. In this system, an antenna systemof one receiving system, for example 1350, is selected as a referenceand includes an antenna pattern 1355 directed to receive the desiredsignal 1360 along a direct path. Each of the remaining receivingsystems, as represented by receiving system 1370, has an antenna pattern1310 directed, positioned or electronically altered to containspatial-null 1315 to receive lower power refracted signals 1325 forsubsequent processing.

[0065] The use of a spatial-nulling antenna pattern to detectlower-power refracted signals 1325 is advantageous as it permits thereception of lower-powers signals that provide a greater measurement ofphases changes induces by the wake or wind-shear environment. As shouldbe understood, each of the antenna systems may be independently operatedto maintain a spatial nullity about the direct path as the targetaircraft continues along its flight path. In this case, receivingsystems 1350 and 1370 are operating in cooperation in the angulartracking/alignment and the processing of the received data sense.Tracking of the signal source may be facilitated by the specific antennaimplementation or otherwise obtained from an independent means.

[0066] Although this second embodiment of the invention has beendescribed with regard to a ground-based system, it should be understoodthat the principles of the second embodiment are applicable to theairborne system shown in FIG. 12. Furthermore, it would be understoodthat the antenna pattern of the receiving system may be mechanicallybiased away from the direct signal (off-axis) to prevent or avoidreception of the direct signal energy. Thus, the phase reference pathremains staring at the signal source in order to optimize the integrityof derived phase measurements. The spatial apertures of adjacent signalpaths however are managed in a way to essentially spatially nullelectromagnetic signals directly from the source, while remainingspatially uncontaminated by other signals or reflections of the sourcefrom non-relevant objects.

[0067] In one embodiment, the adjacent path spatial pattern would imagea “halo” of angularity surrounding the source such as to be able toreceive electromagnetic energy over signal paths close in angularity tothe signal source, yet avoiding the high signal amplitude path directlyfrom the source. This embodiment, using spatial nulling of the adjacentpath, emphasizes the detection of wake induced refractivity wherein thewake bends the propagation path from source to receiver by therelatively subtle amounts induced by anticipated wake induced pressure,temperature and humidity non-homogeneities. By blocking the directreceive path, the adjacent signal vectors are dominated by wake inducedeffects, thereby enhancing the sensitivity of the differentialmeasurements leading to wake detection. Nullifying the direct signalpath signals allows the receiver dynamic range to be centered on thesemore subtle signal modulation effects and provides a high contrast orgain for detecting these signals. The receiver antenna array, inconjunction with phase coherent signal beamforming, provides themechanism for both nullifying direct path signals and resolving theangularity of signals arriving in angles close to the direct path.Electronic processing associated with the recording of continuousabsolute spatial angle over time of the modulations of the receivedsignals at relatively close angles.

[0068] It is also contemplated that the halo could itself be spatiallybroken down into separate zones and processed independently in order tolocalize turbulence or further enhance the detectability of a wake.

[0069] Although the invention has been described in a preferred formwith a certain degree of particularity, it is understood that thepresent disclosure of the preferred form has been made only by way ofexample, and that numerous changes in the details of construction andcombination and arrangement of parts may be made without departing fromthe spirit and scope of the invention as hereinafter claimed. It isintended that the patent shall cover by suitable expression in theappended claims, whatever features of patentable novelty exist in theinvention disclosed.

We claim:
 1. A system for determining atmospheric disturbance that mayexist in front of an aircraft comprising: a plurality of sensor arrays,each array containing at least one sensor element including an antennahaving a known beam pattern, and concurrently receiving at least onesignal; a receiving system in communication with a corresponding one ofsaid at least one sensor element in each of said plurality of sensorarrays, said receiving system operable to isolate a same signal fromsaid at least one received signal in each of said plurality of sensorarrays; means for determining a phase value for each of said samesignals; means for determining a rate of phase change for selectedsubsets of said same signals; means for indicating turbulence when saidrate of phase change exceeds a known threshold associated with selectedsubsets of said same received signals.
 2. The system as recited in claim1, wherein said known pattern associated with at least one said sensorarrays is electronically configured to receive substantially a maximumsignal energy of said same signal.
 3. The system as recited in claim 1,wherein said known pattern associated with at least one said sensorarrays is electronically configured to create a spatial null aboutsubstantially a maximum signal energy of said same signal.
 4. The systemas recited in claim 1, wherein said known pattern associated with atleast one said sensor arrays is mechanically positioned to receivesubstantially a maximum signal energy of said same signal.
 5. The systemas recited in claim 1, wherein said known pattern associated with atleast one said sensor arrays is mechanically positioned to create aspatial null about substantially a maximum signal energy of said samesignal.
 6. A method for determining air turbulence which can undesirablyaffect the operation of an aircraft subjected to said turbulencecomprising the steps of: receiving via a plurality of sensor arrays, asignal at a predetermined frequency in an area where said turbulence isexpected, each array containing at least one sensor element, arranged ina known pattern for concurrently receiving said predetermined frequencysignal; processing said received signal at a receiving systemcorresponding to each of said at least one sensor elements; determininga phase value for each received signal; determining a rate of phasechange for selected subsets of said received signals; detecting a phasechange in said received signal due to turbulence; comparing saiddetected phase change with a threshold value; and indicating thepresence of said turbulence when said detected phase change exceeds saidthreshold value.
 7. The method as recited in claim 6, wherein said knownpattern associated with at least one said sensor arrays iselectronically configured to receive substantially a maximum signalenergy of said same signal.
 8. The method as recited in claim 6, whereinsaid known pattern associated with at least one said sensor arrays iselectronically configured to create a spatial null about substantially amaximum signal energy of said same signal.
 9. The method as recited inclaim 6, wherein known pattern associated with at least one said sensorarrays is mechanically positioned to receive substantially a maximumsignal energy of said same signal.
 10. The method as recited in claim 6,wherein said known pattern associated with at least one said sensorarrays is mechanically positioned to create a spatial null aboutsubstantially a maximum signal energy of said same signal.